Interannual sea level variability in the South China Sea and its response to ENSO

Sea level observed by altimeter during the 1993–2004 period, thermosteric sea level from 1945 through 2004, and tide gauge records are analyzed to investigate the interannual variability of sea level in the South China Sea (SCS) and its relationship with ENSO (El Niño and Southern Oscillation). Both the interannual variations of the observed sea level and the thermosteric sea level are closely related to ENSO. An ‘enigma’ that the SST and sea level in the SCS have inverse response to ENSO is revealed. It is found that the thermosteric sea level has an excellent correspondence to seawater temperature at 100 m depth, and their variations are unsynchronized to SST. Detailed analysis denotes that the warming of seawater occurs only in the upper 75 m during and after the mature phase of El Niño, while the cooling appears in the layers deeper than 75 m during El Niño years. The volume transports between the SCS and the adjacent oceans and the anomalous Ekman pumping contribute a lot for the sea level fall in the developing stage of El Niño, while the mass exchange, which is dominated by precipitation, plays a more significant role in the following continuous negative sea level anomalies.     

Steric and mass-induced Mediterranean sea level trends from 14 years of altimetry data

Long-term series of almost 14 years of altimetry data (1992–2005) have been analysed along with Sea Surface Temperature (SST) and temperature and salinity profiles to investigate sea level trends over the Mediterranean Sea. Although sea level variations are mainly driven by the steric contribution, the mass-induced component plays some role in modulating its oscillation. A spatially averaged positive trend of 2.1 ± 0.6 mm/year has been observed, but a change in sign in 2001 seems to appear. Steric effects (mainly on thermal origin) account for  55% of sea level trend. Although Mediterranean Sea is a semi-enclosed basin, this value is comparable to that reported for the global ocean. Sea level rise is particularly important in the Levantine basin south of Crete with values up to 10 ± 1 mm/year. Other areas of sea level rise are localised throughout the Levantine basin and in the Adriatic and Alboran Seas, with more moderate values. Sea level drop areas are localised in the Algerian basin, between the Balearic Islands and the African coasts and, particularly, in the Ionian basin. In this area, negative trends as high as − 10 ± 0.8 mm/year are detected mainly due to the mass-induced contribution, which suggests decadal changes of surface circulation. The inferred sea level trends have been correlated with North Atlantic Oscillation (NAO) indices and a low but significant correlation has been detected between sea level in the Levantine and Balearic basins and NAO index.     

Reconstruction of past decades sea level using thermosteric sea level, tide gauge, satellite altimetry and ocean reanalysis data

This study investigates past sea level reconstruction (over 1950–2003) based on tide gauge records and EOF spatial patterns from different 2-D fields. In a first step, we test the influence on the reconstructed signal of the 2-D fields temporal coverage. For that purpose we use global grids of thermosteric sea level data, available over 1950–2003. Different time spans (in the range 10–50 yr) for the EOF spatial patterns, and different geographical distributions for the 1-D thermosteric sea level time series (interpolated at specific locations from the 2-D grids), are successively used to reconstruct the 54-year long thermosteric sea level signal. In each case we compare the reconstructed trend map with the reference. The simulation indicates that the longer the time span covered by the spatial EOFs, the closer to the reference the reconstructed thermosteric sea level trends. In a second step, we apply the method to reconstructing 2-D sea level data over 1950–2003, combining sparse tide gauge records available since 1950, with EOF spatial patterns from different sources: (1) thermosteric sea level grids over 1955–2003, (2) sea level grids from Topex/Poseidon satellite altimetry over 1993–2003, and (3) dynamic height grids from the SODA reanalysis over 1958–2001. The reconstructed global mean sea level trend based on thermosteric EOFs (case 1) is significantly lower than the observed trend, while the interannual/decadal sea level fluctuations are well reproduced. Case 2 (Topex/Poseidon EOFs over 1993–2003) leads to a global mean sea level trend over the 54-year time interval very close to the observed trend. But the spatial trends of the reconstruction over 1950–2003 are significantly different from those obtained with thermosteric EOFs. Case 3 (SODA EOFs over 1958–2001) provides a reconstruction trend map over 1950–2003 that differs significantly from the previous two cases. We discuss possible causes for such differences. For the three cases, on the other hand, reconstructed spatial trends over 1993–2003 agree well with the regional sea level trends observed by Topex/Poseidon.     

Reconstruction of Mediterranean sea level fields for the period 1945–2000

The distribution of sea level in the Mediterranean Sea is recovered for the period 1945–2000 by using a reduced space optimal interpolation analysis. The method involves estimating empirical orthogonal functions from satellite altimeter data spanning the period 1993–2005 that are then combined with tide gauge data to recover sea level fields over the period 1945–2000. The reconstruction technique is discussed and its robustness is checked through different tests. For the altimetric period (1993–2000) the prediction skill is quantified over the whole domain by comparing the reconstructed fields with satellite altimeter observations. For past times the skill can only be tested locally, by validating the reconstruction against independent tide gauge records. The reconstructed distribution of sea level trends for the period 1945–2000 shows a positive peak in the Ionian Sea (up to 1.5 mm yr^− 1) and a negative peak of − 0.5 mm yr^− 1 in a small area to the south-east of Crete. Positive trends are found nearly everywhere, being larger in the western Mediterranean (between 0.5 and 1 mm yr^− 1) than in the eastern Mediterranean (between 0 and 0.5 mm yr^− 1). The estimated rate of mean sea level rise for the period 1945–2000 is 0.7 ± 0.2 mm yr^− 1, i.e. about a half of the rate estimated for global mean sea level. These overall results do not appear to be very sensitive to the distribution of tide gauges. The poorest results are obtained in open-sea regions with intense mesoscale variability not correlated with any tide gauge station, such as the Algerian Basin.     

A new insight on the decreasing sea level trend over the Ionian basin in the last decades

Altimetry measurements over the Ionian region and tide gauge records along the southern Italian coasts have been combined to analyse the negative sea level trend over the Ionian basin in the last decades. The apparent decreasing trend should be better understood as an abrupt sea level drop in 1998 probably linked to changes in the surface circulation in the Ionian basin induced by the Eastern Mediterranean Transient, which changed from anticyclonic to cyclonic about March 1998. From then onwards, a rising rate of 7.9 ± 0.9 mm/year is observed over the basin.     

Comparison of Mediterranean sea level fields for the period 1961–2000 as given by a data reconstruction and a 3D model

Two Mediterranean sea level distributions spanning the last decades are examined. The first one is a reconstruction of sea level obtained by a reduced-space optimal interpolation applied to tide gauge and altimetry data. The second distribution is obtained from a 3D (baroclinic) regional circulation model. None of the two representations includes the mechanical atmospheric forcing. Results are presented for two different periods: 1993–2000 (for which altimetry data are available) and 1961–2000 (the longest period common to both distributions).The first period is examined as a test period for the model, since the reconstruction is very similar to altimetry observations. The modelled sea level is in fair agreement with the reconstruction in the Western Mediterranean and in the Aegean Sea (except in the early nineties), but in the Ionian Sea the model departs from observations. For the whole period 1961–2000 the main feature is a marked positive trend in the Ionian Sea (up to 1.8 mm yr^− 1), observed both in the reconstruction and in the model. Also the distribution of positive trends in the Western Mediterranean (mean value of 1.1 mm yr^− 1) and the smaller trends in the Aegean Sea (0.5 mm yr^− 1) are similar in the reconstruction and in the model, despite the first implicitly accounts for sea level variations due to remote sources such as ice melting and the second does not. The interannual sea level variability associated with key regional events such as the Eastern Mediterranean Transient is apparently captured by the reconstruction but not by the model (at least in its present configuration). Hence, the reconstruction can be envisaged as a useful tool to validate further long-term numerical simulations in the region.     

Climate changes detected through the world's longest sea level series

The sea level series of Stockholm in the Baltic Sea, commencing already in 1774, is analysed in various ways together with contemporary climate data, in order to investigate long-term sea level changes and their relations to climate changes.First, a study of the eustatic rise of sea level, based on annual mean sea levels, is peformed, and compared with other sea level and climate studies. It is concluded that the general climatic rise of sea level has increased significantly (99.9%) from about 0.0 mm/year during the end of the Little Ice Age, to about 1.0 mm/year during the past century, characterized by melting of glaciers. Such sea level changes due to northern hemisphere climate variations since 800 A.D. have (hitherto) probably always kept within −1.5 and +1.5 mm/year, with an average fairly close to zero.Second, an investigation of the sea level variability, also based on annual mean sea levels, is performed together with temperature and wind variabilities. It is found that the interannual sea level variability of the Baltic Sea has decreased significantly (98%) from the end of the 1700s to the beginning of the 1900s; after that it has increased significantly (95%) again. Precisely the same is found to apply to winter climate or, more specifically, to the interannual winter temperature variability and the interannual winter wind variability. The common origin of all these long-term changes turn out to be two consecutive winter wind processes over the North and Baltic Seas, especially the Baltic entrance. From the end of the 1700s to the beginning of the 1900s, there has been a rapidly decreasing number of dominating winter winds from northeast, and after that there has been an increasing number of dominating winter winds from southwest. This may indicate corresponding long-term changes in the North Atlantic Oscillation.Third, using monthly mean sea levels together with corresponding wind data, seasonal variations are investigated. The seasonal sea level variation in the Baltic Sea has increased significantly (99%) since the early 1800s, together with a shift of the maximum from late summer to early winter. It is found that the main origin is a secular change of the winter wind conditions over the Baltic entrance, with increasing southwesterly winds in early winter. This might also be related to a long-term change in the North Atlantic Oscillation.     

Sea level forcing in the Mediterranean Sea between 1960 and 2000

Sea level trends and inter-annual variability in the Mediterranean Sea for the period 1960–2000 is explored by comparing observations from tide gauges with sea level hindcasts from a barotropic 2D circulation model, and two full primitive equation 3D ocean circulation models, a regional one and the Mediterranean component of a global one,. In the 2D model, 50% of the sea level variance was found to result from the wind and atmospheric pressure forcing. In the 3D models, 20% of the sea level variance was explained by the steric effects. The sea level residuals at the tide gauges locations, calculated by subtraction of the 2D model output from the sea level observations are significantly correlated (r = 0.4) with the steric signals from the 3D models. After the removal of the atmospheric and the steric contributions the tide-gauge sea level records indicate a period where sea level was stable (1960–1975) and a period where sea level was rising (1975–2000) with rates in the range 1.1–1.8 mm/yr. A part of the residual trend can be explained by the contribution of local land movements (0.3 mm/yr) while its major part indicates a global signal, probably mass addition, appearing after 1975.     

Land water storage contribution to sea level from GRACE geoid data over 2003–2006

Seasonal and inter-annual change in land water storage (expressed in terms of water volume change) over 27 large river basins worldwide are estimated from monthly GRACE geoids solutions computed at GFZ from February 2003 to February 2006. The largest annual water volume change is found in the Amazon basin, followed by the Parana, Ob, Orinoco, Tocantins, Niger, Congo, Ganges, Mekong, and Brahmaputra. In terms of trend over the 3-year period, positive and negative values are observed but in a number of cases computed trends are at the noise level. However significant negative trends are found in the Amazon, Ganges, Mississippi, Nile, Parana, and Zambezi basins, indicating water mass loss over that period. Positive trends (water mass gain) are marginally significant. We have computed the land water contribution to sea level change. On average over the 3-year time span, we find that the net effect is positive (net loss of water in terrestrial reservoirs), on the order of 0.19 +/− 0.06 mm/yr. If sustained over a longer time span than considered here, such a value may become comparable to the ice sheets contribution to sea level rise.     

Geochemical composition of inner shelf Quaternary sediments in the northern South China Sea with implications for provenance discrimination and paleoenvironmental reconstruction

Sediment samples were collected from a borehole in the northern South China Sea with the depositional age back to 400 ka BP, for grain size and geochemical analyses to constrain the sediment provenance and paleoenvironmental variability. Geochemical indices of Th/Sc, Ti/Nb and Th/Nb ratios suggest that the Zhujiang (Pearl River) was the main provenance of the inner shelf sediments of Hong Kong deposited during interglacial periods, whereas the locally-derived granitoids contributed significantly to the exposed inner shelf through the incision of local streams during glacial periods. Furthermore, the influence of the Zhujiang-derived sediments on the inner shelf of Hong Kong varied spatially and temporally with different sea-level changes during the past 400 kyr. Chemical weathering indices suggest hot and wet climate conditions were dominant in South China during interglacial periods of marine isotope stages (MIS) 7, 9 and 11 whereas a dry and cold paleoclimate prevailed during glacial periods of MIS 6 which accounts for weak chemical weathering and coarse-grained deposition on the inner shelf. The Holocene and last interglacial period did not see more intense chemical weathering in the Zhujiang drainage basin than other interglacial periods. Although the high resolution paleoenvironmental changes can not be easily reconstructed due to ubiquitous unconformity in the sedimentary strata and weak age controls compared to the deep sea sedimentation, the present study sheds new lights on the understanding of the transport process of the Zhujiang sediment in the deep ocean and provides a teleconnection of East Asian palaeomonsoon activity between South China, the inland and open sea areas.     

Ecological and morphological response of brackish tidal marshland to the next century of sea level rise: Westham Island, British Columbia

In response to climatic warming, eustatic sea level has been predicted to rise by about 50 cm in the next century. While feedbacks between vegetation growth and sediment deposition tend to allow marshes to maintain their morphology under a constant rate of sea level rise, recent observations of marsh deterioration suggest that changes in the rate of sea level rise may induce loss of economically and ecologically important marshland. We have developed a three dimensional model of tidal marsh evolution that couples vegetation growth and sediment transport processes including bed accretion and wave erosion. We use the model to simulate the response of marshes and tidal flats along the Fraser River Delta, British Columbia to 100 yr forecasts of sea level change. Under low sea level-rise scenarios, the delta and its marshes prograde slightly, consistent with historical measurements. While accretionary processes greatly mediate the response to increased rates of sea level rise, vegetation zones transgress landward under median and high sea level rise rate scenarios. In these scenarios, low marsh erosion and constriction of high marsh vegetation against a dyke at its landward edge result in a 15–35% loss of marshland in the next century. Several important behavioral changes take place after 2050, suggesting that predictions based on field observations and short term model experiments may not adequately characterize (and sometimes underestimate) long-term change. In particular, the replacement of highly productive high marsh vegetation by less productive low marsh vegetation results in continued reduction of the system's total biomass productivity, even as the rate of loss of vegetated area begins to decline.     

Discussion on sea level fluctuations along the Adriatic coasts coupling to climate indices forced by solar activity: Insights into the future of Venice

The North Atlantic Oscillation (NAO), which is a dominant circulation pattern in Northern Hemisphere winter, is known to affect sea-level variability in the Mediterranean Sea mainly through the hydrostatic response of water masses to pressure anomalies and changes in evaporation/precipitation budgets. In this study the influence of the NAO on sea levels along the Adriatic coasts is re-assessed in the attempt to uncover the potential causes of the observed high sensitivity of the northern basin to NAO fluctuations. The investigation is focused on the role of the NAO as forcing factor of the winds blowing in the area and of the freshwaters input from the Po River, both of which influence the hydrodynamics of the Northern Adriatic. In addition, some insights into the future of Venice are discussed on the basis of the hypothesis that NAO phases are modulated by the varying solar activity through the intensity of the Earth's geomagnetic activity.     

The glacial–interglacial paradox: the relation between the global means of sea level and sea surface temperature

Sea level variability during the Quarternary is simulated using a stochastic climate model, and a sensitivity relation for the change in net oceanic evaporation due to a change in sea surface temperature. In the application of this relation, it is assumed that the greater part of the change in net oceanic evaporation causes changes in the land ice storage, rather than being directly returned to the ocean by rivers. The analysis suggests that the observed sea level changes can be interpreted as due to the transfer of heat to the deep ocean from the surface mixed layer, arising from random radiation perturbations of the same variance as would give rise to the interannual variability of the global temperature series. The paradox is that glacial conditions (increase in ice storage) are favoured by positive (temperate) sea surface temperature anomalies, and interglacial conditions (decrease in ice storage) by negative (temperate) sea surface temperature anomalies. The evolution of both these regimes, which are inherently unstable, appears to be controlled by the deep water formation process, while albedo feedback is of minor importance. Fluvial feedback, (in which as the ice storage increases the fluvial inflow decreases), however, is found to be an important process, and a small sensitivity of river inflow to storage is consistent with forcing by random variability or by astronomical forcing. A simple analytical model incorporating the key processes of oceanic evaporation and fluvial feedback is presented. The analysis points to the importance of an accurate river model for climate system modelling.     

Mid–late Holocene monsoon climate retrieved from seasonal Sr/Ca and δO records of Porites lutea corals at Leizhou Peninsula, northern coast of South China Sea

South China Sea (SCS) is a major moisture source region, providing summer monsoon rainfall throughout Mainland China, which accounts for more than 80% total precipitation in the region. We report seasonal to monthly resolution Sr/Ca and δ¹⁸O data for five Holocene and one modern Porites corals, each covering a growth history of 9–13 years. The results reveal a general decreasing trend in sea surface temperature (SST) in the SCS from 6800 to 1500 years ago, despite shorter climatic cycles. Compared with the mean Sr/Ca–SST in the 1990s (24.8 °C), 10-year mean Sr/Ca–SSTs were 0.9–0.5 °C higher between 6.8 and 5.0 thousand years before present (ky BP), dropped to the present level by 2.5 ky BP, and reached a low of 22.6 °C (2.2 °C lower) by 1.5 ky BP. The summer Sr/Ca–SST maxima, which are more reliable due to faster summer-time growth rates and higher sampling resolution, follow the same trend, i.e. being 1–2 °C higher between 6.8 and 5.0 ky BP, dropping to the present level by 2.5 ky BP, and reaching a low of 28.7 °C (0.7 °C lower) by 1.5 ky BP. Such a decline in SST is accompanied by a similar decrease in the amount of monsoon moisture transported out of South China Sea, resulting in a general decrease in the seawater δ¹⁸O values, reflected by offsets of mean δ¹⁸O relative to that in the 1990s. This observation is consistent with general weakening of the East Asian summer monsoon since early Holocene, in response to a continuous decline in solar radiation, which was also found in pollen, lake-level and loess/paleosol records throughout Mainland China. The climatic conditions 2.5 and 1.5 ky ago were also recorded in Chinese history. In contrast with the general cooling trend of the monsoon climate in East Asia, SST increased dramatically in recent time, with that in the 1990s being 2.2 °C warmer than that 1.5 ky ago. This clearly indicates that the increase in the concentration of anthropogenic greenhouse gases played a dominant role in recent global warming, which reversed the natural climatic trend in East Asian monsoon regime.     

Coral Sr/Ca and Mg/Ca records in Con Dao Island off the Mekong Delta: Assessment of their potential for monitoring ENSO and East Asian monsoon

The climate of the South China Sea (SCS) is dominated by the East Asian monsoon (EAM) and can be related to the El Niño-Southern Oscillation (ENSO) owing to the interaction between ENSO and the EAM. An annually-banded coral (Porites sp.) collected from Con Dao Island in the southern SCS was measured for Sr/Ca and Mg/Ca ratios at near-monthly resolution through the annual bands of AD 1948–1999. This island is only ~ 90 km from the Mekong Delta coast and thus significantly influenced by riverine discharge, suggesting relatively severe environmental stress on corals. The Sr/Ca time series shows a clear annual cyclicity chiefly modulated by sea-surface temperature (SST), whereas the Mg/Ca time series exhibits an indistinct annual cyclicity, indicating that the previously-proposed coral Mg/Ca thermometry is greatly disturbed. An instrumental SST record in Con Dao Island (since 1980) has been compared with the Sr/Ca time series to calibrate a Sr/Ca thermometer. The Sr/Ca vs. SST comparison shows that the Sr/Ca thermometer is sometimes disturbed by some factor and that almost all of the disturbances occur around the annual-maximum SST in the warm/wet season. The Sr/Ca data around the annual-minimum SST in the cool/dry season is almost free from the disturbance and thus useful as a SST proxy. The disturbances of the Sr/Ca and Mg/Ca thermometers may be ascribed to the Mekong River discharge and its accompanying phenomena (i.e., large freshwater input, suspended-sediment loads, intense phytoplankton blooms, etc.), which are likely to disturb coral physiological processes. Applying the Sr/Ca thermometer to the whole Sr/Ca time series provides a SST reconstruction from 1948 through 1999. Reconstructed annual-minimum SSTs show a clear quasi-biennial oscillation significantly correlated with ENSO, indicating that the annual-minimum SST in the southern SCS tends to be higher (lower) in El Niño (La Niña) phases. This is compatible with previous observations that the East Asian winter monsoon is weakened (strengthened) in El Niño (La Niña) phases. The reconstructed SST record suggests a warming of 1.0 °C for the latter half of the 20th century. The Sr/Ca and Mg/Ca time series exhibit similar decadal-to-bidecadal variations, which do not seem to be primarily due to SST variability but rather due to some other factor possibly related to disturbance or fluctuation of coral physiological processes. Although both of our Sr/Ca and Mg/Ca data are affected, to a greater or lesser extent, by some non-temperature factor, a part of the Sr/Ca data provides a useful SST proxy and suggests that coral-based SST reconstruction in the southern SCS may be an effective means for monitoring the EAM and ENSO.     

Decadal to millennial cyclicity in varves and turbidites from the Arabian Sea: hypothesis of tidal origin

We have analyzed a Late Holocene record, almost 5000 years long, consisting of varved sediments deposited in the oxygen-minimum zone (OMZ) off Pakistan. We searched for cyclicity in the series of varve thickness (“varve” cycles), of unusually large excursions in varve thickness (“agitation” cycles), and of abundance of turbidites (“turbidite” cycles). We found the following high-frequency cycles (periods between 10 and 100 years) in one or several of the three types of series as follows: near 12.4, 14–15, 16.8, 18.6 (strong, agitation), 25–26 (strong, turbidite), 29–31 (strong, agitation), 39 (varve), 44 (strong, turbidite), 51–54 (strong, agitation), 56 (strong, varve), 64 (strong, turbidite), 69, 77 (strong, turbidite), 82 (very strong, agitation), and 95 years (strong, varve). Low-frequency cycles center around 99–115, 125 (very strong, varve), 164, 177, 202, 242–255 (strong, agitation and turbidite), 280 (strong, varve; doubled, turbidite), 340–370 and 460–490 years.Some cycles of varve thickness match the cyclicity of turbidite frequency (12.3, 14–15, 25–26, 245–255 years) but similarities between spectra are not striking. Taken as a whole, however, the sequence of cycles detected (by autocorrelation and standard Fourier analysis) seems to contain a large proportion of multiples of the basic tidal cycles 4.425 (lunar perigee cycle) and 9.3 years (lunar half-nodal cycle). This impression is supported by testing the three binned spectra for whole-number multiples and fractions as well as whole-number beat structure. We therefore propose that a large proportion of the cyclicity detected can be ascribed to tidal action. Our record also contains evidence for the presence of the 1470-year cycle previously reported from the glacial-age Greenland ice record. The main harmonics of this Greenland cycle can be tied to the pattern of periods seen in the varved sediments. We hypothesize that tidal action produces the cycle, and that the reason for its great length is the requirement that maximum tidal activity has to fall into a narrow seasonal window to be geologically effective.     

Principal components in active galactic nuclei variability data and the estimation of the flux contributions from different components

It has been found that the near-infrared flux variations of Seyfert galaxies satisfy relations of the form   F_i ≈α _{i j} +β _{i j} F_j   , where F_i , F_j are the fluxes in filters i and j ; and  α _{i , j} , β _{i , j}   are constants. These relations have been used to estimate the constant contributions of the non-variable underlying galaxies. The paper attempts a formal treatment of the estimation procedure, allowing for the possible presence of a third component, namely non-variable hot dust. In an analysis of a sample of 38 Seyfert galaxies, inclusion of the hot dust component improves the model fit in approximately half the cases. All derived dust temperatures are below 300 K, in the range 540–860 K or above 1300 K. A noteworthy feature is the estimation of confidence intervals for the component contributions: this is achieved by bootstrapping. It is also pointed out that the model implies that such data could be fruitfully analysed in terms of principal components.     

A full-sky prediction of the Sunyaev–Zeldovich effect from diffuse hot gas in the local universe and the upper limit from the WMAP data

We use the Point Source Catalogue Redshift Survey galaxy redshift catalogue combined with constrained simulations based on the IRAS 1.2-Jy galaxy density field to estimate the contribution of hot gas in the local universe to the Sunyaev–Zeldovich (SZ) effect on a large scale. We produce a full-sky healpix map predicting the SZ effect from clusters as well as diffuse hot gas within  80  h ⁻¹ Mpc  . Performing cross-correlation tests between this map and the WMAP data in pixel, harmonic and wavelet space we can put an upper limit on the effect. We conclude that the SZ effect from diffuse gas in the local universe cannot be detected in current cosmic microwave background (CMB) data and is not a large-scale contaminating factor  (ℓ < 60)  in studies of CMB angular anisotropies. We derive an upper limit for the mean temperature decrement of  Δ T < 0.33 μK  at the 2σ confidence level for the 61-GHz frequency channel. However, for future high-sensitivity experiments observing at a wider range of frequencies, the predicted large-scale SZ effect could be of importance.     

Sensitive response of desert vegetation to moisture change based on a near-annual resolution pollen record from Gahai Lake in the Qaidam Basin, northwest China

We present a 50-year pollen record at near-annual resolution from Gahai Lake in the Qaidam Basin on the northeastern Tibetan Plateau. Chronology of a 22-cm short core was established by ²¹⁰Pb and ¹³⁷Cs analysis. The pollen results at 0.5 cm intervals show large changes in Artemisia/Chenopodiaceae (A/C) ratios from < 0.2 to 0.95 in the last 50 years. High (low) A/C ratios represent increase (decrease) in steppe pollen production, which correspond to high (low) relative humidity observed at nearby Delingha weather station. On the basis of good correspondence with instrumental records and carbonate content from Gahai Lake, we conclude that A/C ratio is sensitive to moisture change and can be a very useful index in reconstructing paleoclimate of arid regions. Comparison with pollen and snow accumulation data from Dunde ice core suggests that effective moisture at low and high elevations shows the opposite relationship when mountain precipitation was extremely high, possibly due to topography-induced uplifting and subsiding air dynamics.